Update sample 5 for QGIS 3.x

[ThomasG77]

Remaining bug is when I click on button show or hide, I got a segmentation fault. Using GDB, I get the following trace.

Thread 1 "timtut5" received signal SIGSEGV, Segmentation fault.
QgsRubberBand::reset (this=0x7400780074, geometryType=QgsWkbTypes::PolygonGeometry) at ../../src/gui/qgsrubberband.cpp:104
104	../../src/gui/qgsrubberband.cpp: No such file or directory.

I do not have any qgsrubberband.cpp file installed with QGIS packages. I do not understand why it's looking for a cpp file as there is already the function within the libqgis_gui.so as I've confirmed that nm -gDC /usr/lib/libqgis_gui.so |grep "QgsRubberBand::reset" returns 0000000000bb64a0 T QgsRubberBand::reset(QgsWkbTypes::GeometryType)

I've compiled against current QGIS libs e.g my log from cmake

cmake -DCMAKE_BUILD_TYPE=Debug ..
-- Found QGIS Core: /usr/lib/libqgis_core.so
-- Found QGIS Gui: /usr/lib/libqgis_gui.so
-- Found QGIS Plugins Dir: QGIS_PLUGIN_DIR-NOTFOUND
-- Found GDAL: /usr/lib/libgdal.so
-- Found GEOS: /usr/lib/x86_64-linux-gnu/libgeos_c.so (3.7.1)
-- Configuring done
-- Generating done
-- Build files have been written to: /home/thomasg/git/QGIS-Code-Examples/5_using_rubber_band_with_canvas/build

[pblottiere]

@ThomasG77 the segmentation fault should be resolved 🤞

[ThomasG77]

Thanks. Was completely stuck...